1. Field of the Invention
This invention generally relates to a linear motion guide unit, and, in particular, to a quad guide-way linear motion guide unit having four guide ways between a rail and a slider to provide an endless relative motion therebetween. More specifically, the present invention relates to an improved multi-guideway linear motion guide unit particularly suitable for use in machining tools, industrial robots or the like as a reciprocating linear motion guide mechanism.
2. Description of the Prior Art
An endless linear motion guide unit is well known. Also well known is a quad guideway endless linear motion guide unit relatively compact in size and having four guide ways between a rail and a slider so as to provide an increased rigidity and accuracy, which is particularly suitable for use as a reciprocating linear motion guide mechanism of various machining tools, industrial robots or the like, which are subjected to intense vibrations and impulsive forces. A typical example of such a quad guideway endless linear motion guide unit is described in Japanese Patent Laid-open Pub. No. 60-139912.
A quad guideway endless linear motion guide unit described in the above-mentioned patent publication is illustrated in FIGS. 9 and 10. As shown in FIG. 9, this prior art guide unit includes a pair of guide rails A and B, which are arranged in parallel as spaced apart from each other, two pairs of sliders C-D and E-F, each pair slidably mounted on a corresponding one of the pair of guide rails A and B, and a slide table Y which is fixedly mounted on these two pairs of sliders C through F. Thus, the slide table Y may move back and forth along the pair of guide rails A and B as indicated by a double-sided arrow G.
FIG. 10 illustrates on an enlarged scale a sliding contact structure between one side of guide rail A and a center block or casing L of either of sliders C and D. As shown in FIG. 10, the guide rail A has a pair of oppositely inclined upper and lower guide surfaces H and I on one side thereof, and since the guide rail A is symmetrical in structure, it also has another pair of oppositely inclined guide surfaces (not shown) on the opposite side thereof. In the illustrated structure, the upper inclined guide surface H is inclined to face generally downward and the lower inclined guide surface I is inclined oppositely to face generally upward.
All of the sliders C through F are identical in structure, and, as shown in FIG. 9, each of these sliders C through F includes a center block or casing L and a pair of front and rear end blocks Q and R fixedly attached to the front and rear ends of the center block of casing L. As well known in the art, each of the sliders C through F is provided with four endless circulating paths, each of which includes a load path section, a return path section and a pair of curved connecting path sections connecting the corresponding ends of the load and return path sections. Each of the endless circulating paths is filled with a plurality of rollers, and these rollers provide a rolling contact between the guide rail and the slider when located in the load path section of the endless circulating path.
As best shown in FIG. 10, each of the sliders C through F is generally inverted-U-shaped structure and thus includes a horizontal section and a pair of vertical sections extending downward from the opposite sides of the horizontal section. Each of the vertical sections is formed with a pair of endless circulating paths, each of which is filled with a plurality of rollers M and N. Described more in detail, in the structure shown in FIG. 10, a pair of endless circulating paths is formed in one leg or vertical section of the slider, and these two endless circulating paths are arranged in an interleaved fashion. That is, one of the endless circulating paths includes a load path section defined by a pair of oppositely facing guide surfaces H and J, a return path section O, and a pair of curved connecting path sections S connecting the corresponding ends of the load and return path sections. In addition, the other endless circulating path includes a load path section defined by a pair of oppositely facing guide surfaces I and K, a return path section P, and a pair of curved connecting path sections T connecting the corresponding ends of the load and return path sections. These load and return path sections H-J, I-K, O and P are formed inside the center block or casing L and the associated curved connecting path sections S and T are formed in the end blocks Q and R.
As shown in FIG. 10, an upper load path section defined by the oppositely facing guide surfaces H and J is located above a lower load path section defined by the oppositely facing guide surfaces K and I, and, furthermore, the return path section P is located above the return path section O. As a result, the curved connecting path sections S and T, which belong to the interleaved different endless circulating paths, are disposed in a crossed arrangement.
However, in the structure described above, difficulty was encountered in forming the rectangularly shaped return path sections O and P at high accuracy and in obtaining a precise alignment between the curved connecting path sections S and T formed in each of the end blocks Q and R and the load and return path sections formed in the center block or casing L when assembled.
In order to cope with the above-mentioned problems, a proposal was made to form a pair of circularly shaped holes U and V in the leg or vertical section of the center block or casing L and then fitting a sleeve W or X, which has been previously formed with a rectangularly shaped return path section P or O, into the corresponding one of such holes U and V. However, even in this case, the alignment problems between the center block or casing L and the associated end blocks Q and R and the sleeves W and X and between the curved connecting path sections S and T and the return path sections 0 and P still remained. In addition, there was a problem of increased sliding resistance against cylindrical rollers M and N using grease as a lubricant within the return path sections O and P.